The present disclosure relates to a method for controlling the speed of a vehicle.
Various types of vehicles of today include a drive train for driving the vehicle and a speed control arrangement for controlling the speed of the vehicle. As such, when an operator of the vehicle requests a certain speed, for instance by actuating the accelerator pedal (or gas pedal), the speed control arrangement communicates with the drive train such that the drive train operates in a working condition in which the requested speed is obtained.
However, there is a risk that the requested speed is not preferred for the vehicle. Purely by way of example, the requested speed may result in that the drive train operates in a working condition that has inappropriately high power losses in for instance a power supply and/or a transmission arrangement of the drive train. As another example, the requested speed may result in an undesired wear of components of the vehicle. In a further example, the requested speed may result in inappropriate vibrations of, and/or noise from, at least some components of the vehicle.
In an attempt to solve the above problems, U.S. Pat. No. 7,789,795 proposes that the engine speed of a power supply is selected so as to correspond to an optimum power supply efficiency and that the ratio of automatic transmission arrangement is selected so as to correspond to a requested power demand.
However, although the '795 method may result in some operating conditions of the drive line in which the power losses of the drive train are relatively low, the '795 method may also result in operating conditions in which the power losses are relative large. An example of an operating condition wherein the power losses in the drive line are above a preferred value may be when the selected engine speed and the requested velocity of the vehicle result in a ratio of the automatic transmission arrangement which ratio is associated with relatively large power losses.
In view of the above, it is desirable to obtain a vehicle control method wherein a drive line of the vehicle, at least during some steady state operating conditions, is operated such that preferred operating conditions are obtained.
As such, the present disclosure relates according to an aspect thereof to a method for controlling the speed of a vehicle. The vehicle comprises a drive train for driving the vehicle and the vehicle also comprises a predetermined preferred speed set. The method comprises:                determining whether or not a substantially constant speed of the vehicle is requested;        if it is determined that a substantially constant speed is requested, determining whether the requested speed lies within or outside of the predetermined preferred speed set, and        if it is determined that the requested speed lies outside of the predetermined speed set, automatically adjusting the speed of the vehicle to a vehicle speed that is within the predetermined speed set.        
A method according to the above implies that the vehicle will obtain a substantially constant speed that lies within the predetermined speed set and this in turn implies that the vehicle will be operated in a preferred operating condition when travelling at a substantially constant speed.
As used herein, the expression “speed set” relates to at least one speed. However, it should be noted that the expression “speed set” may include a plurality of individual speeds. Moreover, in addition to, or instead of, comprising at least one speed, the speed set may comprise one or more speed ranges. As such, the expression “speed set” encompasses any combination of at least one speed and/or at least one speed range.
Optionally, a power loss of the drive train is equal to or below a predetermined power loss within the predetermined preferred speed set.
Optionally, the predetermined preferred speed set comprises a range of preferred speeds, preferably the predetermined preferred speed set comprises a plurality of ranges of preferred speeds.
Optionally, the drive train comprises a power supply and an automatic transmission arrangement which comprises a power split assembly which in turn comprises a step ratio power flow path and a infinitely variable ratio power flow path, at least one value in the predetermined preferred speed set corresponding to at least one condition of the transmission arrangement in which at least a predetermined portion of the power flows through the step ratio power flow path.
Optionally, the predetermined portion of the power flow through the step ratio power flow path is at least 80%, preferably at least 90%, of the power flow through the power split assembly.
Optionally, the vehicle comprises a plurality of predetermined preferred speed sets, the method further comprising:                determining whether the vehicle speed control system requested an acceleration or a deceleration of the vehicle prior to the substantially constant speed request.        
Optionally, if an acceleration of the vehicle was requested prior to the substantially constant speed request and if it is determined that the requested speed lies outside the predetermined preferred speed set:                increasing the speed of the vehicle until it reaches a speed within the preferred speed set.        
Optionally, if an deceleration of the vehicle was requested prior to the substantially constant speed request and if it is determined that the requested speed lies outside of the predetermined preferred speed set:                decreasing the speed of the vehicle until it reaches a speed within the preferred speed set.        
Optionally, the vehicle further comprises a driveline characteristics value input means, the method further comprising:                determining the driveline characteristics value from the driveline characteristics value input means, and        electing the range of preferred speeds in accordance with the driveline characteristics value.        
Optionally, the vehicle further comprises a manual speed control means, the method further comprising:                determining whether or not a substantially constant speed of the vehicle is requested by the manual speed control means.        
Optionally, the vehicle further comprises an automatic speed control means, wherein the step of automatically adjusting the speed of the vehicle comprises a step of operating the automatic speed control means in order to modify the speed of the vehicle.
A second aspect of the present disclosure relates to a computer program product comprising a computer program containing computer program code executable in a computer or a processor to implement the steps of a method according to any of the preceding claims, the product being stored on a computer-readable medium or a carrier wave.
A third aspect of the present disclosure relates to an electronic control unit comprising a computer program product according to the second aspect of the present disclosure and arranged to execute a method for controlling the speed of a vehicle according to the first aspect of the present disclosure.
A fourth aspect of the present disclosure relates to a vehicle comprising a drive train adapted to drive the vehicle, the drive train comprising a power supply and a transmission arrangement. The vehicle comprises an electronic control unit according to the third aspect of the present invention.
Optionally, the vehicle further comprises the driveline characteristics value input means.
Further advantages and advantageous features of the disclosure are disclosed in the following description and in the dependent claims.